CVE-2026-39831

Description

The Verify() method for FIDO/U2F security key types (sk-ecdsa-sha2-nistp256@openssh.com, sk-ssh-ed25519@openssh.com) did not check the User Presence flag. Signatures generated without physical touch were accepted, allowing unattended use of a hardware security key. To restore the previous behavior, return a "no-touch-required" extension in Permissions.Extensions from PublicKeyCallback.

CVSS Metrics

• v3.1•CRITICAL•Score: 9.1CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

EPSS Trends

Current EPSS score: 0.37%• Percentile: 29%

Techniques & Countermeasures

• CWE-862•Missing Authorization

  The product does not perform an authorization check when an actor attempts to access a resource or perform an action.

Affected Systems

• golang•crypto

  < 0.52.0

• golang.org/x•crypto

  < 0.52.0

• golang.org/x/crypto•ssh

  < 0.52.0

• golang.org/x/crypto•golang.org/x/crypto/ssh

  < 0.52.0

References (6)

• https://go.dev/issue/79566
• https://groups.google.com/g/golang-announce/c/a082jnz-LvI
• https://go.dev/cl/781662
• https://pkg.go.dev/vuln/GO-2026-5019
• https://nvd.nist.gov/vuln/detail/CVE-2026-39831
• https://cs.opensource.google/go/x/crypto